YJIT: Implement specialization for no-op {Kernel,Numeric}#dup

Type information in the context for no additional work!

This is the `if (special_object_p(obj)) return obj;` path in
rb_obj_dup() and for Numeric#dup, it's always the identity function.

yjit/bindgen/src/main.rs

@@ -167,6 +167,7 @@ fn main() {
         .allowlist_var("rb_cIO")
         .allowlist_var("rb_cSymbol")
         .allowlist_var("rb_cFloat")
+        .allowlist_var("rb_cNumeric")
         .allowlist_var("rb_cString")
         .allowlist_var("rb_cThread")
         .allowlist_var("rb_cArray")

yjit/src/codegen.rs

@@ -6347,6 +6347,42 @@ fn jit_thread_s_current(
     true
 }
 
+fn jit_numeric_dup(
+    _jit: &mut JITState,
+    _asm: &mut Assembler,
+    _ci: *const rb_callinfo,
+    _cme: *const rb_callable_method_entry_t,
+    _block: Option<BlockHandler>,
+    _argc: i32,
+    _known_recv_class: Option<VALUE>,
+) -> bool {
+    // Numeric#dup has arity=0 and is the identity function.
+    // Our caller already did argument count check, so this is
+    // no-op to return the receiver that is already on the stack.
+    true
+}
+
+/// Specialization for rb_obj_dup() (Kernel#dup)
+fn jit_rb_obj_dup(
+    _jit: &mut JITState,
+    asm: &mut Assembler,
+    _ci: *const rb_callinfo,
+    _cme: *const rb_callable_method_entry_t,
+    _block: Option<BlockHandler>,
+    _argc: i32,
+    _known_recv_class: Option<VALUE>,
+) -> bool {
+    // Kernel#dup has arity=0, and caller already did argument count check.
+    let self_type = asm.ctx.get_opnd_type(StackOpnd(0));
+
+    if self_type.is_imm() {
+        // Method is no-op when receiver is an immediate value.
+        true
+    } else {
+        false
+    }
+}
+
 /// Check if we know how to codegen for a particular cfunc method
 /// See also: [reg_method_codegen].
 fn lookup_cfunc_codegen(def: *const rb_method_definition_t) -> Option<MethodGenFn> {
@@ -10424,6 +10460,8 @@ pub fn yjit_reg_method_codegen_fns() {
         reg_method_codegen(rb_cFloat, "*", jit_rb_float_mul);
         reg_method_codegen(rb_cFloat, "/", jit_rb_float_div);
 
+        reg_method_codegen(rb_cNumeric, "dup", jit_numeric_dup);
+
         reg_method_codegen(rb_cString, "empty?", jit_rb_str_empty_p);
         reg_method_codegen(rb_cString, "to_s", jit_rb_str_to_s);
         reg_method_codegen(rb_cString, "to_str", jit_rb_str_to_s);
@@ -10449,6 +10487,7 @@ pub fn yjit_reg_method_codegen_fns() {
 
         reg_method_codegen(rb_mKernel, "respond_to?", jit_obj_respond_to);
         reg_method_codegen(rb_mKernel, "block_given?", jit_rb_f_block_given_p);
+        reg_method_codegen(rb_mKernel, "dup", jit_rb_obj_dup);
 
         reg_method_codegen(rb_cClass, "superclass", jit_rb_class_superclass);
 

yjit/src/cruby_bindings.inc.rs

@@ -997,6 +997,7 @@ extern "C" {
     pub static mut rb_cInteger: VALUE;
     pub static mut rb_cModule: VALUE;
     pub static mut rb_cNilClass: VALUE;
+    pub static mut rb_cNumeric: VALUE;
     pub static mut rb_cString: VALUE;
     pub static mut rb_cSymbol: VALUE;
     pub static mut rb_cThread: VALUE;